Cutworms on Plants

Symptoms

The first sign most gardeners notice is a seedling or young plant cut off at or just below ground level. Caterpillars clip the seedling stems off there, and you may find several plants in a row left wilted or clipped off.

A few species feed higher up instead, chewing holes in leaves or boring into the heads of lettuce or cole crops. On young plants, look for small, webless perforations in the newly expanding crown leaves. The central growing point of a young plant may be eaten, and that causes serious damage to the crown. Ripening fruit can also show pronounced holes that have been chewed into it.

Normally the caterpillars sit on or just below the soil surface, or on the lower parts of plants. Cutworms are commonly active at night, and older larvae tunnel into the soil during the day. When disturbed, these caterpillars curl into a C-shape. Not every sign appears on every crop, so match what you see to the plant you are growing.

Causes

The damage comes from larvae that live on or just below the soil surface and feed mainly at night. Older larvae drop to the ground and tunnel into the soil during the day, then emerge at night to feed.

Females lay hundreds of eggs, either singly or in clusters. Weedy fields attract more moths to lay their eggs. Control of weeds in and around the planting is called paramount to preventing a serious cutworm problem. Fields that are plowed before planting lose egg-laying sites, food sources, larvae and pupae.

Most cutworms overwinter as young larvae in the soil. They mature and pupate the following spring. Black cutworm moths migrate into an area, and their arrival is tracked using pheromone traps.

Different species feed in different places. Some clip stems near the soil, while a few chew leaves or bore into heads. Strawberry, lettuce and the cole crops are among the plants these larvae feed on.

Diagnosis

Start by looking at where and when the damage happens, because cutworms work at the soil line and at night. Look for stems clipped off at or just below the soil line, which is how cutworms damage seedlings. Check along the row for several plants left wilted or clipped off.

Go out after dark with a flashlight, since the larvae are commonly active at night. In daylight, search on or just below the soil surface or on the lower parts of plants, where the larvae are normally found. Older larvae tunnel into the soil during the day, which is another place to check. When you find a caterpillar, see whether it curls into a C-shape when disturbed.

Holes in leaves or in the heads of lettuce or cole crops point to the few species that feed higher up. Pronounced holes in ripening fruit and small, webless perforations in crown leaves are also described. Weedy fields attract more moths, so look at the weeds around the planting as well.

The sources used for this page name no look-alike problems. What marks cutworms is the pattern in the sources: stems clipped at the soil line, and larvae that feed at night.

Treatments

The cultural steps come first. Destroy crop residues and keep the garden weed-free over winter. Remove weeds from field margins before planting. Control weeds in and around the planting as well, since weed control is paramount to preventing a serious cutworm problem.

Plow fields before planting to destroy egg-laying sites, food sources, larvae and pupae. In a vegetable garden, protect seedlings with cardboard collars, screen or protective cloth. You can also hand-pick cutworms off plants at night using a flashlight. For black cutworm, the sources describe using ecological pest management and cultural strategies to protect crops.

Organic options come next. Larger garden plants can be protected with sprays of Bacillus thuringiensis or spinosad. Organically acceptable sprays containing one of these are listed for cole crops and for strawberries, each as a specific formulation. A spinosad bait that targets cutworms is also listed, as is a Bacillus thuringiensis ssp. kurstaki bait or spray. For either bait, check with an organic certifier to confirm the product is organically acceptable.

Chemical options come last. A carbaryl ground bait is listed for the field edge, where cutworms may migrate from weeds or other crops. A methomyl foliar spray is listed with a wetting agent added to improve coverage.

This page gives no doses, rates or spray intervals. The product label is the legal instruction, and it must be followed for the crop and site being treated.

Prevention

Prevention is mostly about weeds and winter cleanup. Weedy fields attract more moths to lay their eggs, so keeping weeds down in and around the planting removes that draw. Remove weeds from field margins before planting.

Destroy crop residues and keep the garden weed-free over winter. Most cutworms overwinter as young larvae in the soil. Plowing before planting destroys egg-laying sites, food sources, larvae and pupae.

Seedlings and young plants are the ones cut off at or just below ground level. Protect them with cardboard collars, screen or protective cloth. Black cutworm moths migrate into an area, and pheromone traps are used to track their arrival. Ecological pest management and cultural strategies are the approach described for protecting crops from black cutworm.

Plants most often affected

These crops are listed as hosts: strawberry, lettuce, cabbage, broccoli, cauliflower, Brussels sprouts, kohlrabi, corn, wheat and tobacco. Seedlings and young plants are cut off at or just below ground level. Check the symptoms section above for what each kind of damage looks like.

• Aji
• Bermudagrass
• Cayenne Pepper
• Eggplant
• Field Pumpkin
• Garden Cucumber
• Garden Lettuce
• Garden Onion
• Garden Tomato
• Kidney Bean
• Spinach